Low via resistance system

ABSTRACT

A method of forming a metallization interconnection system within a via. A first liner layer of titanium is deposited to a first thickness in the following manner. A substrate containing the via is placed within an ion metal plasma deposition chamber that contains a titanium target. The ion metal plasma deposition chamber is evacuated to a first base pressure. A first flow of argon is introduced to the ion metal plasma deposition chamber at a first deposition pressure. The substrate is biased to a first voltage. A plasma within the ion metal plasma deposition chamber is energized at a first power for a first length of time. A second liner layer of Ti x N y  is deposited to a second thickness on top of the first liner layer of titanium in the following manner. A first flow of nitrogen and a second flow of argon are introduced to the ion metal plasma deposition chamber at a second deposition pressure. The substrate is biased to a second voltage. The plasma within the ion metal plasma deposition chamber is energized at a second power for a second length of time, after which the substrate is removed from the ion metal plasma deposition chamber. Finally, a third liner layer of titanium nitride is deposited in a second deposition chamber, and a plug of tungsten is deposited.

FIELD

[0001] This invention relates to the field of integrated circuitprocessing. More particularly the invention relates to a system forreducing contact resistance between metallic interconnection layers in avia structure.

BACKGROUND

[0002] Vias are structures that are formed to enable electrical contactbetween different electrical interconnection layers in an integratedcircuit. The via is typically formed in an insulating layer that isdisposed between the two electrical interconnection layers, so thatelectrical contact only occurs at predetermined locations between thetwo electrical interconnection layers. The via is typically an etchedhole that has a relatively high aspect ratio, meaning that it tends tobe much deeper than it is wide. This is especially true as devicegeometries continually shrink.

[0003] Typically, a via is filled with a metallic electrical conductionsystem that makes contact between the underlying conduction layerdisposed below the insulating layer in which the via is formed and theoverlying conduction layer disposed above the insulating layer in whichthe via is formed. In a typical process, several different layers ofmetallic materials are used to fill the via. A thin titanium liner layeris first deposited as an adhesion layer and as a gettering layer. A thintitanium nitride liner layer is then deposited as a barrier layer toprotect the underlying layers during subsequent processing. Finally, atungsten plug is deposited to completely fill the via.

[0004] Because the via is a relatively small structure, it is importantto reduce any electrical resistance created within the via by as great adegree as possible. One source of electrical resistance within the viais contact resistance between the metallic layers of the system asdescribed above, such as can be caused by oxidation of the surfaces ofthe various layers. Oxidation of a layer tends to occur whenever thelayer is exposed to the atmosphere, such as when it is transported fromthe chamber in which an underlying layer is deposited to the chamber inwhich an overlying layer is deposited. Oxidation is a particular problemwith the titanium liner layer, which oxidizes very quickly in thepresence of oxygen.

[0005] What is needed, therefore, is a system for reducing the contactresistance in a via by reducing the oxides that form on the titaniumliner layer.

SUMMARY

[0006] The above and other needs are met by a method of forming ametallization interconnection system within a via. A first liner layerof titanium is deposited to a first thickness in the following manner. Asubstrate containing the via is placed within an ion metal plasmadeposition chamber that contains a titanium target. The ion metal plasmadeposition chamber is evacuated to a first base pressure. A first flowof argon is introduced to the ion metal plasma deposition chamber at afirst deposition pressure. The substrate is biased to a first voltage. Aplasma within the ion metal plasma deposition chamber is energized at afirst power for a first length of time.

[0007] A second liner layer of Ti_(x)N_(y) is deposited to a secondthickness on top of the first liner layer of titanium in the followingmanner. A first flow of nitrogen and a second flow of argon areintroduced to the ion metal plasma deposition chamber at a seconddeposition pressure. The substrate is biased to a second voltage. Theplasma within the ion metal plasma deposition chamber is energized at asecond power for a second length of time, after which the substrate isremoved from the ion metal plasma deposition chamber. Finally, a thirdliner layer of titanium nitride is deposited in a second depositionchamber, and a plug of tungsten is deposited.

[0008] Because the second liner layer of Ti_(x)N_(y) is deposited in thesame chamber as the first liner layer of titanium, there is noopportunity for the first liner layer of titanium to oxidize to titaniumoxide, which prevents the problems as described above. Further, becausethe Ti_(x)N_(y) is deposited using ion metal plasma deposition, there isno cusping at the top of the via structure, which further prevents theproblems as described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Further advantages of the invention are apparent by reference tothe detailed description when considered in conjunction with the FIGURE,which is not to scale so as to more clearly show the details, and whichdepicts a partial cross-sectional view of a via filled with ametallization interconnection system according to the present invention

DETAILED DESCRIPTION

[0010] Referring now to the figure, there is depicted a metallizationinterconnection system 10, constructed according to a preferredembodiment of the present invention. The metallization interconnectionsystem 10 is deposited within a via 11 that is defined between sidewalls20, such as would be formed in a dielectric layer. The metallizationinterconnection system 10 makes ohmic contact between a lower conductionlayer 22 and an upper conduction layer that is not depicted.

[0011] The first layer in the metallization system 10 is a first linerlayer of titanium 12. The first liner layer of titanium 12 functions asa gettering layer to clean out impurities that may be present in the via11. The first liner layer of titanium 12 is preferably deposited usingan ion metal plasma deposition method.

[0012] During ion metal plasma deposition, atoms of the metal to bedeposited are sputtered from a target and ionized in a plasma with adensity of between about 10¹⁰ ions/cm³ and about 10¹³ ions/cm³, and mostpreferably about 10¹² ions/cm³. The metal ions are then drawn in ahighly directional manner toward the substrate by an electrical bias onthe substrate, and are uniformly deposited across the surfaces of thesubstrate, as mentioned above. Ion metal plasma deposition, such asdescribed herein, can be performed in a deposition chamber such as theVectra chamber that is integrated on the Endura cluster tool platform,as manufactured by Applied Materials, Inc. of Santa Clara, Calif.

[0013] Ion metal plasma deposition is a physical vapor depositiontechnique that produces a film that is visually distinguishable fromthose deposited by other physical vapor deposition techniques, in thatit produces a film that has better coverage at the bottom of the via andless top side wall coverage. In other words, films deposited using ionmetal plasma deposition have good step coverage in comparison to filmsproduced by other physical vapor deposition techniques. For example,other forms of physical vapor deposition, such as sputtering, tend toproduce films that cusp at the top edges of the via 11. This cusping ofthe deposited film tends to get increasingly worse as additional filmsare deposited, and often results in an inability to completely fill thevia 11. This situation creates several problems with the integratedcircuit, and is preferably avoided.

[0014] Thus, the first liner layer of titanium 12 as depicted in thefigure has very good step coverage. As mentioned above, thecross-sectional profile of the ion metal plasma deposited first linerlayer of titanium 12 is immediately distinguishable from other physicalvapor deposition techniques, which produced a cusped film.

[0015] To deposit the first liner layer of titanium 12, the substrate onwhich the via 11 is disposed is brought into an ion metal plasmadeposition chamber containing a titanium target, and the ion metalplasma deposition chamber is evacuated to a first base pressure. Thefirst base pressure is preferably between about 10⁻⁹ Torr and about 10⁻⁶Torr, and most preferably about 5×10⁻⁹ Torr. A first flow of argon isthen introduced to the ion metal plasma deposition chamber. The firstflow of argon is preferably between about 0.5 sccm and about 200 sccm,and most preferably about 20 sccm. The valving leading to the vacuumpumps on the ion metal plasma deposition chamber is adjusted to producea first pressure inside of the ion metal plasma deposition chamber ofbetween about 10⁻⁴ Torr and about 0.1 Torr, and most preferably about30×10⁻³ Torr.

[0016] The substrate is biased to a first voltage of between about 0volts and about −500 volts, and most preferably about −150 volts, and aplasma is ignited within the ion metal plasma deposition chamber at afirst power of between about 1 kilowatts and about 50 kilowatts, andmost preferably about 5 kilowatts. A direct current power supply is usedto provide the power to ignite the plasma in the preferred embodiment.However, in other embodiments a radio frequency power supply may beused. In a most preferred embodiment the substrate is held at a firsttemperature of between about −50 centigrade and about 400 centigrade,and most preferably about 200 centigrade, during the ion metal plasmadeposition of the first liner layer of titanium 12.

[0017] The deposition of the first liner layer of titanium 12 proceedsfor a first length of time, which is preferably a period of time ofbetween about 1 seconds and about 100 seconds, and most preferably about20 seconds. Ion metal plasma deposition for this length of time underthe conditions specified above produces a first liner layer of titanium12 with a thickness of between about 5 angstroms and about 1,000angstroms, and most preferably about 150 angstroms.

[0018] After the deposition of the first liner layer of titanium 12, asecond liner layer of Ti_(x)N_(y) is deposited. As described above, ifthe first liner layer of titanium 12 is exposed to oxygen, such as bybringing the substrate out of the ion metal plasma deposition chamberand into the atmosphere, then the first liner layer of titanium 12oxidizes at the surface and forms a layer of titanium oxide. The layerof titanium oxide increases the resistance within the metallizationinterconnection layer 10, and creates problems with the integratedcircuit of which it is a part. Thus, it is preferred to cap the firstliner layer of titanium 12 in some manner, prior to exposing thesubstrate to the atmosphere.

[0019] In the preferred embodiment of a method according to the presentinvention, this is accomplished by depositing a second liner layer ofTi_(x)N_(y) 14 on top of the first liner layer of titanium 12. Thesecond liner layer of Ti_(x)N_(y) 14 is preferably deposited in the sameion metal plasma deposition chamber as that which is used to deposit thefirst liner layer of titanium 12. In this manner, there is noopportunity for the first liner layer of titanium 12 to be exposed tooxygen and form a titanium oxide layer. In an alternate embodiment, thesecond liner layer of Ti_(x)N_(y) 14 is deposited within a separate ionmetal plasma deposition chamber within the same cluster tool in whichthe ion metal plasma deposition chamber for the first liner layer oftitanium 12 resides. In this manner, the substrate is again not exposedto the atmosphere between depositions of the first liner layer oftitanium 12 and the second liner layer of Ti_(x)N_(y) 14.

[0020] It is noted that the second liner layer of Ti_(x)N_(y) 14 isdeposited using only ion metal plasma deposition, and not any other formof physical vapor deposition or any form of chemical vapor deposition.Some of the purposes for this selection of deposition technique are toreduce the degree of cusping that is inherent with other forms ofphysical vapor deposition, as described elsewhere in this discussion,and further to reduce the oxidation of the first liner layer of titanium14 that are attendant with exposing the first liner layer of titanium 14to the atmosphere, and may be attendant with various forms of chemicalvapor deposition, even if the first liner layer of titanium 14 is notexposed to the atmosphere prior to such deposition.

[0021] To deposit the second liner layer of Ti_(x)N_(y) 14, a first flowof nitrogen is introduced to the ion metal plasma deposition chamber.The first flow of nitrogen is preferably between about 1 scem and about200 seem, and most preferably about 100 sccm. The first flow of argon ispreferably adjust to a second flow of argon at a flow rate of betweenabout 0.5 sccm and about 100 sccm, and most preferably about 20 sccm. Ina most preferred embodiment, the flow rate of the first flow of argon isgradually changed to the flow rate of the second flow of argon, ratherthan halting the first flow of argon and then commencing the second flowof argon. The valving leading to the vacuum pumps on the ion metalplasma deposition chamber is adjusted to produce a second pressureinside of the ion metal plasma deposition chamber of between about 10⁻⁴Torr and about 0.1 Torr, and most preferably about 30×10⁻³ Torr.

[0022] The substrate is biased to a second voltage of between about 0volts and about 400 volts, and most preferably about −150 volts. In amost preferred embodiment, the first voltage is gradually changed to thesecond voltage, rather than halting the first voltage and then applyingthe second voltage. A plasma is ignited within the ion metal plasmadeposition chamber at a second power of between about 1 kilowatts andabout 50 kilowatts, and most preferably about 2 kilowatts. In a mostpreferred embodiment, the first power applied to the plasma is graduallyadjusted to the second power applied to the plasma, rather than shuttingoff the first power and then re-igniting the plasma with the applicationof the second power.

[0023] As before, a direct current power supply is used to power theplasma in the preferred embodiment. However, in other embodiments aradio frequency power supply may be used. In a most preferred embodimentthe substrate is held at a second temperature of between about −50centigrade and about 400 centigrade, and most preferably about 200centrigrade, during the ion metal plasma deposition of the second linerlayer of Ti_(x)N_(y) 14.

[0024] The deposition of the second liner layer of Ti_(x)N_(y) 14proceeds for a second length of time, which is preferably a period oftime of between about 0.1 seconds and about 100 seconds, and mostpreferably about 5 seconds. Ion metal plasma deposition for this lengthof time under the conditions specified above produces a second linerlayer of Ti_(x)N_(y) 14 with a thickness of between about 1 angstromsand about 300 angstroms, and most preferably about 20 angstroms. At theend of this deposition, the plasma is preferably extinguished, and thesubstrate is removed from the ion metal plasma deposition chamber.

[0025] Because of the introduction of the first flow of nitrogen intothe ion metal plasma deposition chamber, the second liner layer ofTi_(x)N_(y) 14 can be formed in the same chamber in which the firstliner layer of titanium 12 is formed. The second liner layer ofTi_(x)N_(y) 14 acts as a capping layer to the first liner layer oftitanium 12, because the second liner layer of Ti_(x)N_(y) 14 does notoxidize as readily when exposed to oxygen. Therefore, the substrate maybe safely removed from the ion metal plasma deposition chamber at thispoint without fear of oxidizing the first liner layer of titanium 12 andcreating the problems as described above.

[0026] Because the second liner layer of Ti_(x)N_(y) 14 is depositedusing the ion metal plasma deposition process as described above, it isvisually distinguishable from Ti_(x)N_(y) layers that are deposited withother physical vapor deposition techniques, such as sputtering. This isbecause the other physical vapor deposition techniques tend to producecusping of the deposited layer at the top of the via 11, as describedabove, whereas the ion metal plasma deposition produces a layer that hasgood step coverage. The second liner layer of Ti_(x)N_(y) 14, asdeposited using ion metal plasma deposition, is also visuallydistinguishable from layers that are deposited using chemical vapordeposition. Thus, a layer deposited with ion metal plasma deposition isphysically distinguishable from a layer that is deposited using anotherdeposition method. The metallization interconnection system 10 asdescribed above is further physically distinguishable from othermetallization systems in that there is no titanium oxide layer on top ofthe first liner layer of titanium 12.

[0027] The second liner layer of Ti_(x)N_(y) 14 is purposely recitedherein without a specific stoichiometry, because the processingconditions described above do not necessarily produce a film that has asingle, set stoichiometry. As described elsewhere, the purpose of thesecond liner layer of Ti_(x)N_(y) 14 is not to have a specificstoichiometry, but rather to provide a capping layer to the first linerlayer of titanium 12, so that it does not oxidize, and to do so in amanner that will not produce cusping and the problems attendant withcusping. This can be accomplished with a wide range of stoichiometriesof the second liner layer of Ti_(x)N_(y) 14. However, in a preferredembodiment of the invention, the value for X is between about 0.45 andabout 0.8, and most preferably about 0.5, while the value for Y isbetween about 0.55 and about 0.2, and most preferably about 0.5.

[0028] To complete the metallization interconnection system 10, a thirdliner layer of titanium nitride (TiN) 16 is deposited with astoichiometry that is more definitely set as compared to the secondliner layer of Ti_(x)N_(y) 14, and which is deposited such as by using achemical vapor deposition method. The stoichiometry of the third linerlayer of titanium nitride 16 is preferably more definitely set becausethe third liner layer of titanium nitride 16 is intended to function asa barrier layer during later processing, and thus the third liner layerof titanium nitride 16 requires certain physical properties, such aschemical resistance, that are attendant with its set stoichiometry.Finally, the via 11 is filled with a tungsten plug 18, such as may beformed with a chemical vapor deposition. The metallizationinterconnection system 10 is then preferably planarized and theprocessing of the substrate continues.

[0029] The foregoing description of preferred embodiments for thisinvention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise form disclosed. Obvious modifications orvariations are possible in light of the above teachings. The embodimentsare chosen and described in an effort to provide the best illustrationsof the principles of the invention and its practical application, and tothereby enable one of ordinary skill in the art to utilize the inventionin various embodiments and with various modifications as is suited tothe particular use contemplated. All such modifications and variationsare within the scope of the invention as determined by the appendedclaims when interpreted in accordance with the breadth to which they arefairly, legally, and equitably entitled.

What is claimed is:
 1. A metal interconnection system disposed within avia, comprising: a first liner layer of ion metal plasma depositedtitanium, a second liner layer of ion metal plasma depositedTi_(x)N_(y), a third liner layer of chemical vapor deposition titaniumnitride, and a plug of tungsten.
 2. The metal interconnection system ofclaim 1, wherein the first liner layer of ion metal plasma depositedtitanium has a thickness of between about 5 angstroms and about 1000angstroms.
 3. The metal interconnection system of claim 1, wherein thesecond liner layer of ion metal plasma deposited Ti_(x)N_(y) has athickness of between about 1 angstroms and about 3000 angstroms.
 4. Amethod of forming a metal interconnection system within a via,comprising the sequential steps of: depositing a first liner layer oftitanium using ion metal plasma deposition in an ion metal plasmadeposition chamber, depositing a second liner layer of Ti_(x)N_(y) usingion metal plasma deposition in the ion metal plasma deposition chamber,depositing a third liner layer of titanium nitride using chemical vapordeposition in a second deposition chamber, and depositing a plug oftungsten.
 5. The method of claim 4, wherein the first liner layer of ionmetal plasma deposited titanium is deposited to a thickness of betweenabout 5 angstroms and about 1000 angstroms.
 6. The method of claim 4,wherein the second liner layer of ion metal plasma deposited Ti_(x)N_(y)is deposited to a thickness of between about 1 angstroms and about 300angstroms.
 7. A method of forming a metallization interconnection systemwithin a via, comprising the steps of: depositing a first liner layer oftitanium to a first thickness by; placing a substrate containing the viawithin an ion metal plasma deposition chamber that contains a titaniumtarget, evacuating the ion metal plasma deposition chamber to a firstbase pressure, introducing to the ion metal plasma deposition chamber afirst flow of argon at a first deposition pressure, biasing thesubstrate to a first voltage, and energizing a plasma within the ionmetal plasma deposition chamber at a first power for a first length oftime, depositing a second liner layer of Ti_(x)N_(y) to a secondthickness by; introducing to the ion metal plasma deposition chamber afirst flow of nitrogen and a second flow of argon at a second depositionpressure, biasing the substrate to a second voltage, energizing theplasma within the ion metal plasma deposition chamber at a second powerfor a second length of time, and removing the substrate from the ionmetal plasma deposition chamber, depositing a third liner layer oftitanium nitride in a second deposition chamber, and depositing a plugof tungsten.
 8. The method of claim 7, wherein the first flow of argonfurther comprises a flow of between about 0.5 sccm and about 200 sccm.9. The method of claim 7, wherein the first deposition pressure furthercomprises a pressure of between about 10⁻⁴ Torr and about 0.1 Torr. 10.The method of claim 7, wherein the first voltage further comprises avoltage of between about 0 volts and about −400 volts.
 11. The method ofclaim 7, wherein the first power further comprises a power of betweenabout 1 kilowatts and about 50 kilowatts.
 12. The method of claim 7,wherein the first length of time further comprises a length of time ofbetween about 1 seconds and about 100 seconds.
 13. The method of claim7, wherein the first flow of nitrogen further comprises a flow ofbetween about 1 sccm and about 200 sccm.
 14. The method of claim 7,wherein the second flow of argon further comprises a flow of betweenabout 0.5 sccm and about 100 sccm.
 15. The method of claim 7, whereinthe second deposition pressure further comprises a pressure of betweenabout 10⁻⁴ Torr and about 0.1 Torr.
 16. The method of claim 7, whereinthe second voltage further comprises a voltage of between about 0 voltsand about −400 volts.
 17. The method of claim 7, wherein the secondpower further comprises a power of between about 1 kilowatts and about50 kilowatts.
 18. The method of claim 7, wherein the second length oftime further comprises a length of time of between about 0.1 seconds andabout 100 seconds.
 19. The method of claim 7, wherein the firstthickness further comprises a thickness of between about 5 angstroms andabout 1000 angstroms.
 20. The method of claim 7, wherein the secondthickness further comprises a thickness of between about 1 angstroms andabout 300 angstroms.